Electrochemical cells provide electrical energy that powers a host of electronic devices such as external and implantable medical devices. Among the many medical devices powered by electrochemical cells are leadless pacemakers. Leadless pacemakers are typically cylindrically shaped devices that are inserted into the body through a circular catheter and attached directly to heart tissue. Leadless pacemaker devices contain both the device circuitry and electrical power source in one container. In some embodiments, the electrochemical cell power source may comprise up to 80 percent of the volume of a leadless pacemaker device. In addition, leadless pacemaker devices are designed to operate within the body for an extended period of time, as long as 10 years or more. Thus, it is desirable to provide an electrochemical cell having a reduced size without sacrificing energy capacity of the cell. Such an electrochemical cell having a reduced size with increased energy density would, therefore, enable the development of less invasive miniaturized leadless pacemakers as well as other medical devices that require a relatively small electrical power source with increased capacity.
Prior art electrochemical cells designed to power miniaturized medical devices, such as a leadless pacemaker, are generally of a bobbin-type construction as illustrated in FIG. 3. While bobbin-type electrochemical cell constructions provide reliable discharge characteristics, such constructions are not optimally designed to provide maximum energy density as compared to the electrochemical cell design of the present invention. For example, prior art bobbin-type cell constructions typically comprise a gap between the anode and cathode that extends along the length of the cell. In contrast, the electrochemical cell of the present invention is constructed in a “piston-type” configuration in which the anode/cathode interface is oriented perpendicular to the length of the cell. Such a cell construction of the present invention thus reduces the electrode interfacial area in comparison to a bobbin-type cell construction, which helps to increase the overall energy density of the cell.
In addition, the cathode of cylindrically shaped cells, may radially expand within the casing during discharge. Radial expansion of the cathode is not desired as the expanding cathode can interfere with the intended operation of the cell.
Thus, the electrochemical cell of the present invention is constructed having a cathode current collector of a variety of shapes and configurations designed to minimize radial expansion of the cathode and instead encourage axial expansion of the cathode within the casing.
Thus, as will be discussed in more detail hereinafter, the cathode assembly of the present invention comprises a unique structure that provides a lithium electrochemical cell with increased energy density.